ANOVA tests main effects and interactions for significance.Īn ANOVA Summary Table for these data is shown in Table 2.Ĭonsider first the effect of "Weight." The degrees of freedom (df) for "Weight" is 1. What is important is what the sample data allow you to concludeĪbout the population. The important questions are not whether thereĪre main effects and interactions in the sample data. These simple effects are not significantly different. In thisĮxample, the simple effects of weight are 0.54 and 0.44. Is an interaction when the simple effects differ. Of one variable differs depending on the level of another variable. Recall that there is an interaction when the effect Of Weight at the level of "Acquaintance" isīetween the "Acquaintance Typical" and the "Acquaintance The difference between the "Girlfriend Typical" and the "Girlfriend Obese" conditions. The simpleĮffect of Weight at the level of "Girlfriend" is Of the variable at a single level of another variable. Simple effect of a variable is the effect In contrast to a main effect, which is theĮffect of a variable averaged across levels of another variable, The marginal means for "Girlfriend" and "Acquaintance" are 5.92 and Is based on a comparison of these two marginal means. Similarly, the marginal mean for the level "Typical" is the That this marginal mean is equal to the mean of 5.65 and 6.15, The marginal mean for the level "Obese" is the mean Mean of the means of all levels of the other variable. A marginal mean for a level of a variable is the It is convenient to talk about main effects in terms of marginal A main effect of an independent variable is theĮffect of the variable averaging over the levels of the other variable(s). The first two effects (Weight and Relationship) are both mainĮffects. Weight x Relationship Interaction: Does the effect of weightĭiffer depending on the relationship with the companion?.On their relationship with their companion? Relationship: Are applicants judged differently depending.Weight: Are applicants judged differently depending on the.There are three effects of interest in this There would be an interaction between the obesity factor and Is a girlfriend than if she is just an acquaintance. Prejudice against a person with an obese companion if the companion The effect of having an obese companion would differ depending Variable differs depending on the level of a second variable. There is an interaction when the effect of one Moreover, there is a much bigger advantage than efficiencyįor including two variables in the same study: it allows a test It is more efficient to conduct one study that includes both independent Two separate studies, one with each independent variable. Typical weight and (2) whether the companion was a girlfriend Variables were investigated: (1) whether the companion was obese or of Study, the researchers were interested in whether the weight ofĪ companion of a job applicant would affect judgments of a maleĪpplicant's qualifications for a job. Compute the source of variation and df for each effect in a factorial.State the relationship between simple effects and interaction.Define main effect, simple effect, interaction, and marginal mean.